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34C3 preroll music
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Christoph Sieg: The idea is now to go from[br]space back to earth and try to use drones
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– so autonomous flying vehicles – for[br]power generation. So this is the second
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part. So the outline here is …[br]Applause
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Christoph: Thank you very much.[br]Applause
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Christoph: So the outline is that first I[br]will introduce the source here and
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motivate why it is a good idea to harvest[br]high altitude winds and produce energy
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from them. The technological part will[br]come in the second part here. This is
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about the technology which is called[br]airborne wind energy. And in a third part
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I want to show how you can build a wind[br]drone for low cost for yourself and
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experiment with this kind of technology.[br]So let's start with the first part. And
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here as a reminder is the conventional[br]energy supplier wish list, so probably
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what your global players in conventional[br]energy would think about it or tell you:
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They would say that is a surely clean-[br]enough resource and, meaning on timescales
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here, it is exploitable of the order of[br]one human life expectancy, it's
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controllable especially economically and[br]politically, it is depreciable
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economically and it leads so to a very[br]high profit for some players.
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Unfortunately there's also the[br]technological part and here sometimes it's
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driven by hope, saying it will be OK. But,[br]as we know, it might be mostly harmless.
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So as we see here for instance there are[br]catastrophes like Chernobyl. This is after
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the catastrophe where you have the[br]memorial for the people who died. Then you
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have scenarios during the catastrophe[br]here. This is Deepwater Horizon being like
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desperately tried to extinguish the fire[br]by the US Coast Guard and Fire Brigades.
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And of course – what I don't have to[br]mention here, but in times of fake news
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it's important to mention – we are before[br]the catastrophe. So this is here a plot of
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the carbon dioxide concentration in the[br]atmosphere taking from ice. And as you see
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here the ice ages give this variations[br]over 500,000 years, and now we are at this
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spot here that points up. And if you[br]resolve this into the time scale, extent
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this time scale from the last thousand to[br]2,000 years here – so we are here at this
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spot at 2000, year 2000 – then you see[br]that this rise has started at the
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industrialization. So it's a clear sign[br]that we have to do something. And we have
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to do it quickly.
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Applause
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Christoph: So now let's try to propose[br]something which can be part of the
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solution, namely sustainable energies. And[br]here's a wish list of what probably you
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would think it should be: It should be[br]sustainable, ubiquitous, continous,
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accessible and profitable at the very end.[br]So does such a source exist? And first I
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should define what it means. So[br]sustainable means it should serve present
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needs without compromising the future –[br]and this is clearly not what we are doing
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now – so it should be available on[br]timescales which are like the lifetime of
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our central star if possible. It should be[br]ubiquitous, meaning that it should be
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present almost on any location on earth so[br]that we can without a very complicated
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long-range infrastructure have access to[br]the energy. It should be continuous,
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meaning it should be present at almost any[br]day time and seasons, so that we can plan
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of what we produce. And of course it[br]should be accessible, meaning it can be
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tapped by the technology and lead to a[br]significant contribution to our energy
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mix. And profitable should of course also[br]be. So does it exist? And the answer is
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yes and I want to show that this airborne[br]wind energy can be a big part of it. So
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here I have a table of some sustainable[br]energy sources and the wishlist items are
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written here and I put some of the[br]sustainable sources. So there is fusion,
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there is solar energy – terrestrial and[br]also the spacial energy which was
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presented by Anja and by Stefan before –[br]hydro energy, geothermal energy and
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conventional wind energy; where by[br]conventional wind energy I mean wind
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energy up to approximately 100 meter which[br]is the hub height of wind turbines,
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approximately. And as you can see some of[br]these items here are not fulfilled by all
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these different approaches. So for example[br]the spacial energy is clearly not
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ubiquitous, because you have this beam as[br]we heard which is just like basically
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hitting a certain spot on the earth and[br]there are transferred into energy, so you
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have to distribute this energy. Also it is[br]not yet accessible. On the other hand wind
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energy – here conventional wind energy –[br]is not ubiquitous, because you can only
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select certain spots. And it is not[br]continuous, because you cannot really plan
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when the wind is blowing and when it's not[br]blowing. So let's add to this list what is
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called high altitude wind. And high[br]altitude wind is clearly sustainable,
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because it's also wind energy – so it's[br]like driven as all the other wind energy
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as well. And high altitude here means to[br]go to heights which are above 200 meters
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and try to drain energy from these winds.[br]So let me argue why it is a ubiquitous
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source. And for this Philip who is also[br]here and part of the team – I'm very happy
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he has made this very nice plot here which[br]shows the western part of Europe and it
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shows the ratio of wind power which you[br]can extract at an optimal height which
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should be below 1,000 meter – so this is[br]just an arbitrary at the moment limit – to
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say that we can have a system which can[br]basically get up to thousand meter height
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and compare it to the wind energy which is[br]basically available at hundred meter. And
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in this plot you can see at the coastline[br]there is a line here and this line is the
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line where in the interior you have[br]already a doubling of the wind power. So
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meaning at the coast line itself if you go[br]to higher altitude you have the double
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wind power available then at hundred[br]meter. Even better, directly at the coast
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line there is another line which is a[br]factor of four better. So as soon as you
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put your wind turbines on land side, you[br]will be a factor of, you have access to a
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factor of four higher wind power. And[br]here, in the region slightly south of
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Leipzig, there's another line, this is a[br]factor of eight where you become better in
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wind power, in high altitudes wind power.[br]So, seeing that the coastal regions have
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already a factor of four in this ratio[br]better and the inland between four and
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eight. Oh, the wrong sign. Sorry, they[br]should be reversed of course. So, saying
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that here the site of conventional wind-[br]energy harvesting, which are now very
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limited, and where you put for instance[br]all the wind turbines in the north, they
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become much more accessible if you go to[br]higher heights. Because there you can
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basically use all the land sites. So this[br]is where you have more sites available
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when you harvest at optimal height. And[br]here, as an example about why it is a
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continuous source, you see a time[br]distribution of the wind velocity in
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January 2016 in Leipzig. The wind velocity[br]is here increasing from yellow to red, and
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the altitude is displayed here, and this[br]is the time scale of the month. And what
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you can see is, at hundred meter height[br]you have almost like only in the lower
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parts you have winds, whereas, if you go[br]to higher heights you have the reddish
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parts where you have high wind velocities.[br]So this shows that continuity is already
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improved if you go to higher altitude,[br]especially for land sites. And this is
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almost impossible for conventional wind[br]turbines. You would have to build a mast
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higher and much, much bigger structures.[br]And also, what is displayed here is the
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optimal harvesting height. So this is the[br]height, again below thousand meter, where
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it would be optimal to harvest wind at a[br]certain time, displayed over the whole
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month. And if one goes from this plot to[br]the histograms, so to the time
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distribution of the different wind[br]velocities, you get this picture here. So
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this are the spots the histograms of 100,[br]170, 500, 1000 meter, and of the optimal
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height, so if you adjust your height. And[br]one of the things that you can see is that
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the mean is clearly shifted to higher wind[br]velocities if you increase the height. And
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also, if you harvest at optimal altitude[br]you shift the whole probability
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distribution to the right. So and what[br]increases there is that the fraction of
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time below five meter per second, which is[br]like the the time where the cut in wind
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speed for a wind turbine, so you would[br]like starting produce energy, the
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probability to have such winds is[br]increased from 76% to 87%, which is quite
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a lot of increase. So adjusting to varying[br]optimal harvesting height is not only
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almost, but is really impossible for[br]conventional wind turbines. So one has to
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find another technology, which is better[br]and can give you access to this higher
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altitude winds. So this is the plot again[br]from before. So I have now a little bit
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motivated why the source is ubiquitous and[br]continuous. Now the question is, is it
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accessible, and how it is accessible. And[br]this is the technological part which is
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called airborne wind energy. So how do we[br]access these high altitude winds. So on
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for these, let's come back to the design[br]challenges, which would be necessary to go
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to higher height. So high altitude means,[br]that you just cannot just increase your
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tower, and have more torque on your[br]foundation, and just scale up the system.
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So you should avoid proliferation of mass[br]and proliferation of the tower and
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foundation. And also, varying altitude[br]means you shouldn't have passive,
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stabilizing, static structures, but find[br]something which can vary. So just as an
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example here this is the sky walk in the[br]Grand Canyon, and this is already a quite
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scary lever arm which you have. And if, in[br]comparison, you take your modern wind
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turbine, you rotate it by 90 degrees, and[br]compared it in size to this, you can see
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what kind of torque will be, like will act[br]on the foundation. So this is already a
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very big piece of technology you have[br]here. So we have to do better, and this is
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the second part, namely airborne wind[br]energy, so the technology itself. So the
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first slide is probably the most important[br]of this part because it explains the
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idea behind this technology. So you take[br]autonomous drones, which are the most
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flexible connected to the ground via[br]tethers, and extract wind energy via these
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drones. So how does it work? So look at[br]this conventional wind turbine here. You
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have most of the energy is produced by the[br]outer part of the wings. They are rotating
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with the highest velocity, and at the same[br]time you have the highest the largest
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lever arm. So you produce most of the[br]energy in the outer part. The inner part
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is more or less passive, stabilizing[br]structure. So you remove that structure
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and replace it by something which is[br]flexible, and the first which comes to
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mind probably is a tether with which you[br]attach it to the ground. And then you have
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just the active part here, which is now an[br]aircraft, moving in this circle, which
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before was circulated by the wing tips, to[br]extract your energy. This is the
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principle. So how do we bring down the[br]power when circulating this aircraft? So
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we have to, in some way, transform it to[br]electric power. So there are, which are
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not shown in the picture before, lighter[br]than air systems. So you just basically
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take a balloon, you put your wind turbine[br]at high altitude, and extract the power.
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And here the tether can clearly serve as[br]the power line. But what we can also do is
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crosswind flight, which was shown in the[br]picture before. So here you have a moving
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aircraft, which can move in something[br]which is called the drag mode, meaning
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that you have onboard generators on the[br]aircraft. So essentially it's a propeller
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aircraft, but the propellers are reversed[br]in repeller mode, so that the repellers
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produce energy for you. And then the[br]tether serves as power line. So this
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principle is shown here. So here you can[br]see the generators and then the power is
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brought down by the tether. In the second[br]part, second strategy, is using the so
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called lift mode So here you have ground[br]based generators and the tether itself
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transmits the power, there are no power[br]lines in the tether. So here you use that
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the power is given by the pulling force[br]times the reel out velocity of the tether.
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So you circulate in some patterns with[br]your aircraft and you use the lift force
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acting on the aircraft to unreal this[br]tether from a drum, and at the drum, on
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the base station, there's a generator[br]attached which helps you to get the
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energy, to transform the energy into[br]electrical energy. And of course, at some
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point the tether is maximally reeled out[br]and then you have to have to go to a reel
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in phase, where with minimal energy you[br]reel in the tether again, and start
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periodically this phase again. So these[br]are the concepts, and there's a whole zoo
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of airborne wind energy devices and[br]proposals, which show that this technology
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is still in a very early stage of being[br]developed. So you have people here flying
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figure-of-eight patterns with the[br]aircraft. So some things are lighter than
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air turbines, which look very exotic like[br]this one, probably this one you have seen
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in media already. Proposals like this[br]here. There are quad copters, which
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produce the energy by rotating of their,[br]of the propellers here. And all kind of
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exotic lever arm and aircrafts which you[br]can use. So let's bring a little bit of
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more order into the technology, into the[br]proposals. And one of the things I want to
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discuss, which is very promising, is what[br]is called crosswind flight. So here as a
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example is a comparison of a conventional,[br]lighter-than-air system with the big wheel
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in London. So this is one of the biggest[br]wind turbines. And the harvesting area is,
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so the effective area of such a wind[br]turbine is the swept area of your
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propellers, essentially. So now let's look[br]what happens if you move an aircraft
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instead through the wind. Then the picture[br]of before is like of that size. And if you
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take an aircraft, which has the same wing[br]area as the wing areas of the propeller
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here, you're harvesting area is of that[br]size. It's much bigger. And the reason for
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this is, that the effective area is now[br]given by the wing area times a
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coefficient, which is the square fraction[br]of the lift to drag coefficient of the
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aircraft times the lift coefficient[br]itself. And this factors of the order of
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200. So it increases the efficiency of[br]your of your wings dramatically. This was
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already found by Loyd in 1980. And you can[br]now ask "Why does it take 30 years from
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this idea to first systems?". And the[br]answers is, in this community for is
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probably a very interesting is "Why are[br]these prototypes are appearing only 30
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years later?". It's because sufficient[br]computer power. So for the control
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algorithms, which allow you to control[br]such flight modes, was not available. So,
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as an example, here's an illustration of[br]one of the current leaders in the field
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called AMPYX POWER, showing a crosswind[br]airborne wind energy system versus a
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conventional system. So here's the[br]conventional wind turbine for two
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megawatts. And the conventional this is a[br]conventional system. And the airborne wind
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system is, this is the ground station, and[br]this is the aircraft. So one of the things
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which are, I mean, visible in this picture[br]is that it has much less like even sight
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impact in the environment. So having[br]something like this is much less
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disturbing from the even from the[br]aesthetic point of view, than this huge
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wind turbine. So now the next step would[br]be to look closer to the technology and
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see what are the AWE system components[br]that you need, that you need to build such
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a device. So first of all, there is the[br]drone or the fixed-wing aircraft. We have
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seen that it's very good to have large[br]lift and small drag coefficients, so you
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need something which is like a rigid[br]glider, more or less. On board you need
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sensors, like accelerometer, gyroscope,[br]GPS, receiver, barometer, and a pitot tube
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to measure the air the air speed. And this[br]is to determine the system state, that
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then is like reacted on by the control[br]surfaces, in the case of an aircraft by
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ailerons flaps and the rudder. Moreover,[br]you need of course a microcontroller and
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algorithms which do the state estimation.[br]So from the sensor data they compute the
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state of the system, meaning it's[br]position, altitude, velocity. And you have
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to navigate. So and of course you might[br]need something like a propeller for
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takeoff, landing, and energy generation in[br]case of drag mode. The second thing is of
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course the ground station. So here you[br]need the drum for tether wind-up. You need
0:19:03.340,0:19:08.559
a motor which eventually has to be[br]transformed into generator mode if you
0:19:08.559,0:19:12.409
have the lift mode. You need power[br]converters, also microcontrollers and
0:19:12.409,0:19:16.510
algorithms which synchronize your ground-[br]station operation with the drone; and you
0:19:16.510,0:19:22.299
need a runway, catapult or something alike[br]for takeoff and landing. So far it looks
0:19:22.299,0:19:28.320
quite simple, but the devil is in the[br]detail. And here I found a nice quote a
0:19:28.320,0:19:33.510
colleague of mine – (uninteligble name) – [br]has done in one of his talks,
0:19:33.510,0:19:37.170
and I liked it very much because it[br]displays very well what challenges have to
0:19:37.170,0:19:42.600
be still overcome. So it starts with[br]"Theory is when nothing works but everyone
0:19:42.600,0:19:48.100
knows why." and to demonstrate this let's[br]have a look at this video here which is
0:19:48.100,0:19:56.539
one of the flight attempts of one of the[br]companies: So the aircraft lifts off,
0:19:56.539,0:19:58.640
there's no sound … yet. Now there is[br]sound.
0:19:58.640,0:20:02.740
Background music of shown video
0:20:02.740,0:20:05.030
Speaker in shown video:[br]Abort! Abort! Abort!
0:20:05.030,0:20:07.898
Soft laughter
0:20:07.898,0:20:13.110
Christoph: Yeah. And the desperation of[br]the founder was clearly hearable at the
0:20:13.110,0:20:16.750
end. And you could see that the tether[br]ruptured. And then there was no way to
0:20:16.750,0:20:23.120
recover that most of the aircraft was[br]lost. Second: "Sometimes practice is when
0:20:23.120,0:20:27.130
everything works but no one knows why." So[br]there are also positive surprises. And
0:20:27.130,0:20:33.330
here is a launch, a catapult launch, for[br]an aircraft which now uses weight.
0:20:33.330,0:20:43.290
Background noise of shown video[br]Laughter
0:20:43.290,0:20:48.360
Christoph: So a positive surprise for a[br]test. And finally, sometimes if you
0:20:48.360,0:20:52.700
combine theory and practice then "nothing[br]works but no one knows why". This is where
0:20:52.700,0:20:57.210
the complication really is: The devil is[br]in the detail. And here you can see a
0:20:57.210,0:21:00.649
video from a flight which is crosswind[br]flight: Everything seems normal …
0:21:00.649,0:21:14.450
Dramatic background music of shown video[br]Christoph: … and then the prototype is
0:21:14.450,0:21:23.380
again lost. So this is complicated. So but[br]there is a lot of progress and so I want
0:21:23.380,0:21:28.379
to come closely, very quickly introduce[br]the current industrial status. So I focus
0:21:28.379,0:21:32.360
on three companies which work on that: So[br]one of them is Enerkite in Berlin, and
0:21:32.360,0:21:36.640
they have now a system which is basically[br]stationed on such a truck and this is a
0:21:36.640,0:21:41.660
crosswind system of a passive wing. So it[br]steered via three tethers and it produces
0:21:41.660,0:21:47.710
up to 30 kilowatts of energy. Then you[br]have Ampyx Power. They have here the
0:21:47.710,0:21:51.580
launching site in the Netherlands and they[br]are currently producing this aircraft
0:21:51.580,0:21:58.210
here. This type which is a crosswind[br]system in lift mode. And at the end will
0:21:58.210,0:22:04.101
produce up to 250 kilowatts of power. This[br]is under construction. And, finally, there
0:22:04.101,0:22:10.929
is Google X Makani in California. And they[br]have built a drag-mode aircraft – here –
0:22:10.929,0:22:15.750
which is flying. And I can show you a[br]video that they have on their home page –
0:22:15.750,0:22:21.799
very nicely. Where they show a flight so[br]that you can see that the 600 kilowatt
0:22:21.799,0:22:26.700
system is working. Here you see the[br]onboard propellers. You can see the
0:22:26.700,0:22:32.570
tether. Down here this is from the tether[br]attachment point. So the things are
0:22:32.570,0:22:42.970
working. There are prototypes. But one of[br]the things which are important is: one has
0:22:42.970,0:22:47.300
to "test, test, test" and get experience[br]from tests. So "experience is what you get
0:22:47.300,0:22:52.480
when you were expecting something else".[br]You really. So what does it mean? So we
0:22:52.480,0:22:57.299
have to test, analyze, adapt the systems.[br]So because many – as you could see from
0:22:57.299,0:23:01.429
this design variations in the zoo which[br]I've shown – many of the concepts are
0:23:01.429,0:23:06.559
still open. So for example the design of[br]the airframe. If you use a biplane, a
0:23:06.559,0:23:10.190
flying wing or anything alike – or[br]something totally different – is still
0:23:10.190,0:23:14.860
open. The tether construction – what kind[br]of materials to use – is still open. The
0:23:14.860,0:23:20.590
materials in itself is still open for the[br]aircraft etc. etc.. The mode of operation
0:23:20.590,0:23:25.070
– that means takeoff, landing and direct[br]versus lift mode – is still an open
0:23:25.070,0:23:30.299
question. What is the best thing to[br]realize for industrial products? And then
0:23:30.299,0:23:34.649
control hardware and software algorithms[br]have to be tested thoroughly. Of course
0:23:34.649,0:23:40.720
it'd have to be certified by the aerospace[br]agencies, of course. You want to have a
0:23:40.720,0:23:46.119
failsafe. So what you have to do is you[br]want to even, I mean, have total losses in
0:23:46.119,0:23:49.979
experiment. You want to do the experiments[br]wich would lead to a total loss of your
0:23:49.979,0:23:56.210
system. So here comes the idea that[br]instead you should build a cheap and
0:23:56.210,0:24:01.949
disposable test platform instead of a[br]largely scaled-up system first, before you
0:24:01.949,0:24:05.860
build the expensive prototype and do tests[br]on them. And this brought us to the idea
0:24:05.860,0:24:10.559
to provide a low-cost open-source test[br]platform where everybody at home can build
0:24:10.559,0:24:15.890
his own wind drone. And this is the third[br]part of the talk. So the do-it-yourself
0:24:15.890,0:24:24.340
wind drone. What are the ingredients here?[br]So first you need a drone, so here I want
0:24:24.340,0:24:29.120
to show the airframe and reinforcement[br]hack which is necessary to prepare your
0:24:29.120,0:24:33.330
airframe for the additional forces by[br]adding the tether. Then there's a ground
0:24:33.330,0:24:37.740
station and here I want to motivate why[br]the drone is essentially behaving like a
0:24:37.740,0:24:44.110
fish – in this case a barracuda. The next[br]thing is navigation on curved manifold is
0:24:44.110,0:24:48.680
very important because you have like a[br]constraint coming from the tether. And
0:24:48.680,0:24:54.100
finally you need something for control[br]which is the autopilot. So in this case
0:24:54.100,0:25:01.120
it's the ardupilot open-source project[br]which we adapted. So let's come to the
0:25:01.120,0:25:05.890
airframe-reinforcement-hack. So what you[br]use: Take your favourite polystyrene
0:25:05.890,0:25:11.289
airframe – so in this case it's an Easy[br]Star II – and glue the wings together.
0:25:11.289,0:25:15.580
This is the lower side of the wings. You[br]put in there a carbon rod – here in this
0:25:15.580,0:25:21.139
part – and you stabilize it with racks[br]which you glue into the slits we can see
0:25:21.139,0:25:29.179
here. And then you wrap carbon in the[br]forward part of it where the most of the
0:25:29.179,0:25:35.789
aerodynamic force is attached. Then you[br]have the carbon ???? ???? wind around your
0:25:35.789,0:25:44.320
tether. And you install additional tubes[br]for fixing the wings on the fuselage. So
0:25:44.320,0:25:48.610
the fuselage is here. We cut off the[br]engine blocks, included additional carbon
0:25:48.610,0:25:52.639
rods. So you can put these carbon rods on[br]these carbon rods here, and fix everything
0:25:52.639,0:25:59.570
with screws. So to show you how that looks[br]like and what are the size of this model
0:25:59.570,0:26:05.799
is: So here is the original-size aircraft[br]with carbon. And you can later – if you
0:26:05.799,0:26:15.330
want – pass by the assembly area and look[br]at it and have a look at it and touch it.
0:26:15.330,0:26:20.580
So this is how it looks decomposed into[br]different components: So again wings and
0:26:20.580,0:26:27.269
so on and so on, the servos for the[br]control surfaces. The central unit here is
0:26:27.269,0:26:33.150
the Pixhawk autopilot. So there's a[br]microcontroller which contains some of the
0:26:33.150,0:26:37.340
sensors: You have a GPS sensor, in[br]addition you have a telemetry antenna for
0:26:37.340,0:26:45.830
data – for data transfer to the ground[br]station. And you have RC control for
0:26:45.830,0:26:51.580
manual control when you switch out of auto[br]mode to have manual control in emergency
0:26:51.580,0:26:58.740
situations – or if you want to make other[br]kind of flight tests. So now this is the
0:26:58.740,0:27:02.560
drone itself. So now is the question what[br]to do with the ground station. And here
0:27:02.560,0:27:09.250
let's look why the drone behaves as a[br]fish: Because what it does is, like in
0:27:09.250,0:27:13.059
fishing, you would need a free-moving[br]tether; it has to be fast and fail-safe
0:27:13.059,0:27:16.889
reeled in and reeled out; and it should[br]remain twist free so that it doesn't give
0:27:16.889,0:27:21.490
any knots if it is not under tension. And[br]the thing which we came up with wich best
0:27:21.490,0:27:27.559
serves for our needs at the moment is an[br]off-shore fishing reel.
0:27:27.559,0:27:33.769
Applause[br]Christoph: So and you need offshore here
0:27:33.769,0:27:37.889
because the drum has to be perpendicular[br]to the rod: This guarantees you like
0:27:37.889,0:27:42.750
reload phases twist free on the[br]tether. Other fishing rods have the drum
0:27:42.750,0:27:47.549
aligned with the rod, and then you[br]accumulate twist on the tether which can
0:27:47.549,0:27:52.769
lead to knots, lead to knots and then …[br]it's not a good idea. It will destroy your
0:27:52.769,0:27:56.950
tether. So and this is the first flight[br]test. So we were very enthusiastic and
0:27:56.950,0:28:02.650
started the first flight test. And here it[br]is.
0:28:02.650,0:28:13.149
Indistinct voice in shown video[br]Voice in shown video: OK. … Hinterher?
0:28:13.149,0:28:15.139
Laughter[br]Visv: Versuch mal rauszugehen. Manual?
0:28:15.139,0:28:17.789
Achtung, Achtung! Versuch ihn zu fangen.[br]Na gut.
0:28:17.789,0:28:19.779
Beeping in shown video[br]Christoph: OK.
0:28:19.779,0:28:23.259
Laughter[br]Christoph: So unfortunately it did not
0:28:23.259,0:28:27.620
work.[br]Applause
0:28:27.620,0:28:34.720
Christoph: So what happens? This was the[br]result: The tail was broken. And because
0:28:34.720,0:28:38.749
the tether apparently wrapped around the[br]back of the aircraft and then it became
0:28:38.749,0:28:42.700
uncontrollable. So we came up with what do[br]we do: If you don't know any further, any
0:28:42.700,0:28:47.700
better, use carbon! So we put some carbon[br]on the lower part of the of the fuselage
0:28:47.700,0:28:53.499
to reinforce it. And then of course you[br]have to think about writing your
0:28:53.499,0:29:00.019
navigation code, to navigate if you are[br]under tethered flight. So here is the
0:29:00.019,0:29:05.360
receipe for how to do it: So first you[br]take one git clone of ardupilot – this
0:29:05.360,0:29:09.019
autumn open-source software. You[br]take one curved 2-dimensional manifold –
0:29:09.019,0:29:13.700
it's essentially giving us a hypersurface[br]embedded in 3-dimensional Euclidean space.
0:29:13.700,0:29:18.220
In case of constant tether length this is[br]just a semi-hemisphere as to which is
0:29:18.220,0:29:22.160
centered around your ground station. Then[br]you take a planar curve which you want to
0:29:22.160,0:29:28.070
fly along – or curved segments – and a[br]pinch of Differential Geometry to wrap it
0:29:28.070,0:29:32.230
on the sphere, to make this curve[br]appearing on the sphere. You take a little
0:29:32.230,0:29:38.279
bit of Classical Mechanics for the flight[br]control to transfer the curve
0:29:38.279,0:29:45.549
accelerations into actually control-[br]surface motions. And then you need, of
0:29:45.549,0:29:51.559
course, 12 dozen coffee for doing so. You[br]put everything together into – of course
0:29:51.559,0:29:55.620
not the coffee – into the computer algebra[br]system and stir well, and let the CPU bake
0:29:55.620,0:30:03.559
it at 100 degrees, and then you come up[br]with a smooth – at least C¹ – curve.
0:30:03.559,0:30:09.350
Applause[br]Christoph: So the curve is shown here. So
0:30:09.350,0:30:13.820
it's … this is one part of a figure-8[br]pattern. So the other part would be behind
0:30:13.820,0:30:17.949
here. It's composed of two geodesic[br]segments and one turning segment and they
0:30:17.949,0:30:21.720
are C¹ glued together here. And these are[br]the equations: So you can find in the
0:30:21.720,0:30:26.899
paper – I don't want to go into detail. So[br]now you have to modify the source code of
0:30:26.899,0:30:31.450
this ardupilot project. So here there are[br]highlighted the patterns which you
0:30:31.450,0:30:35.289
basically have to … where you have to do[br]modifications: You have to implement new
0:30:35.289,0:30:42.139
flight modes and change some of the[br]control algorithms. And then you come up
0:30:42.139,0:30:49.499
with the next flight test. And here is the[br]next attempt.
0:30:49.499,0:31:11.389
Music and propellor sounds[br]Voice in shown video: Beim Auswerten
0:31:11.389,0:31:28.909
müssen wir sehen, ob wir dann verschiedene[br]wählen.
0:31:28.909,0:31:35.480
Music ends[br]Applause
0:31:35.480,0:31:41.160
Christoph: The whistling sound you have[br]heard at the end is the tether being
0:31:41.160,0:31:45.259
dragged through the air. So there was[br]really tension on the tether. And you can
0:31:45.259,0:31:50.019
also see this if you do a data analysis on[br]the flight data later. So yes for example
0:31:50.019,0:31:54.539
multiple possibilities. You have a lot of[br]data which is possible to analyze. So the
0:31:54.539,0:31:59.610
autopilot this was very very it's very[br]very nicely done in this open-source
0:31:59.610,0:32:04.210
project: So they have a data file with all[br]primary and secondary data you can use for
0:32:04.210,0:32:08.049
your analysis. So for instance this is the[br]flight curve of different flight modes
0:32:08.049,0:32:11.919
which we used. You have the altitude of[br]the aircraft, you can look to deviations
0:32:11.919,0:32:16.440
in radial and transverse directions. You[br]can look to tether tension – or like a
0:32:16.440,0:32:20.621
measure for tether tension – by looking to[br]the length variation of the tether. And
0:32:20.621,0:32:26.519
you can of course do time series analysis[br]of how your figure-8 pattern has flown
0:32:26.519,0:32:33.620
along. And that is what you can do with[br]this very very nice autopilot open-source
0:32:33.620,0:32:40.359
software which is available when … written[br]by many many people on the internet. So
0:32:40.359,0:32:44.019
the question which remains is: After all[br]of this is, will it be a fail-safe to
0:32:44.019,0:32:49.929
100%? And the answer is nope, it will not![br]It will … there will be of course
0:32:49.929,0:32:56.850
accidents happen. But the thing is:[br]Nothing is failsafe. And so here's a
0:32:56.850,0:33:00.960
standard wind turbine and look for[br]yourself.
0:33:00.960,0:33:06.070
Laughter[br]Christoph: You see there is no 100%
0:33:06.070,0:33:15.480
guarantee, but we have to try very hard to[br]get it as failsave as possible. So yeah
0:33:15.480,0:33:20.220
this is essentially it. That was the talk.[br]So what I want to say is that the current
0:33:20.220,0:33:28.919
status of airborne wind energy can be seen[br]here by a nice book on the Springer page
0:33:28.919,0:33:33.499
which you can download here. And we are[br]very very happy to have any kind of
0:33:33.499,0:33:38.280
critical remarks, input to help in[br]developing the system further. So please
0:33:38.280,0:33:41.860
if you want, look to this web page,[br]there's a lot of information including a
0:33:41.860,0:33:48.450
paper and we will be very happy for any[br]kind of help. And finally I would again
0:33:48.450,0:33:52.279
stress that we could rely on this[br]tremendous work of the open-source
0:33:52.279,0:33:56.710
community working on this autopilot[br]project that has helped us to realize this
0:33:56.710,0:34:02.029
project in very short time; so very happy[br]about this. And I want to thank of course
0:34:02.029,0:34:07.040
Phillip Bechtle, who is here, and Thomas[br]Gehrmann and Maximillian Schulz-Herberg,
0:34:07.040,0:34:11.250
the students, and Udo Zillmann, who can[br]not be here, for working on this project
0:34:11.250,0:34:14.980
and putting so much work also into it.[br]Thank you very much for your attention!
0:34:14.980,0:34:17.230
Applause
0:34:17.230,0:34:27.670
H: We can have two more on the microphones
0:34:27.670,0:34:32.900
here and here – one and five – so two[br]questions. The first one, please!
0:34:32.900,0:34:37.380
Question: So you talk, so you talked a lot[br]about powered – and not powered –, but
0:34:37.380,0:34:41.590
controlled flight. How does it compare –[br]energy wise – to uncontrolled flight?
0:34:41.590,0:34:46.400
Basically putting a propellor on a kite?[br]Answer: So the thing is the propellor on
0:34:46.400,0:34:53.909
the kite … with kite you mean, I guess,[br]non-rigid structures. So meaning that the
0:34:53.909,0:35:00.080
first question is how do you want to put a[br]propeller on a kite if it's non rigid. So
0:35:00.080,0:35:07.030
that is a question which goes back to you.[br]So because that is something is not clear
0:35:07.030,0:35:12.170
to me. But in any case rigid air[br]frame is harder to control than a
0:35:12.170,0:35:17.160
kite. So there are people who work with a[br]kite. And by kite surfing or if you do
0:35:17.160,0:35:21.740
like steer normal kites from the ground.[br]You know it's like moving not that fast in
0:35:21.740,0:35:27.130
the wind field, so it's easier to control.[br]This is a big benefit of kites. And also
0:35:27.130,0:35:32.410
the weight is a big benefit. But the power[br]output – because of the bad or worse lift-
0:35:32.410,0:35:37.600
to-drag coefficient – is unfortunately not[br]that efficient as a rigid aircraft. So you
0:35:37.600,0:35:42.280
want to go to the rigid air craft.[br]H: If you leave the room now, please be
0:35:42.280,0:35:45.810
quiet because we have questions and[br]answers here! Number three please, and
0:35:45.810,0:35:50.400
that is the last question I'm afraid. But[br]you can ask questions after the talk.
0:35:50.400,0:35:57.890
Q: I want to go back to the space part. I[br]was wondering … there are some ideas about
0:35:57.890,0:36:03.040
bootstrapping like a solar station on the[br]moon and then like shipping, I don't know,
0:36:03.040,0:36:08.480
hydrogen or like pre-charged lithium[br]batteries back to earth and back and
0:36:08.480,0:36:14.360
forth. Is it like realistic or not really?[br]A by Anja Kohfeldt (previous talk): I
0:36:14.360,0:36:19.280
think also this approach would be quite[br]expensive. And you have to install this
0:36:19.280,0:36:25.630
infrastructure on the moon first, and you[br]have to establish the flight base back and
0:36:25.630,0:36:30.840
forward. Realistic is a thing, you know.[br]At the end that's a question of money and
0:36:30.840,0:36:38.010
investment. And I'm not sure whether this[br]would pay out, but we haven't analyzed
0:36:38.010,0:36:44.500
this kind of approaches, yet.[br]H: Thank you! So thank you very very much
0:36:44.500,0:36:53.100
Stefan, Anja and Christoph! Give them a[br]warm applause again please!
0:36:53.100,0:36:57.210
Applause[br]Stefan: Thank you!
0:36:57.210,0:37:01.750
Outro music
0:37:01.750,0:37:14.236
subtitles created by c3subtitles.de[br]in the year 2019. Join, and help us!